Compensating master cylinder



Nov l?v le@ H. c. BOWEN 23960,@

COMPENSATING MASTER CYLINDER Filed Juan. 25, 1952 Patented Nov'. 17, 1936 t "UNITED .sTArr-:s

PATENT orifice coMPENsA'rING I Mns'rsn cymmnn Herbert C. Bowen, Detroit, Mich., asslxnor to Hydraulic Brake Company, Detroit, Mich., a

I corporation of California Application January 25, 1932, Serial No. 588,594

, 2 Claims.

. and improved compensating master cylinder.

. 'master cylinder; und

Another object is to provide a compensating muster cylinder which will provide freer flow of duid past the piston during thereturn stroke thereof. A Y

Another object is to provide a compensating master cylinder in which e relatively large opening is normally maintained between the master cylinder ond the reservoir.,

.Another object is to provide o, novell piston construction for master cylinders.

Another object is to provide a vertically disnosed master cylinder in .which the highest point in the compression cheminer is normally mein- 'teined in tree communication with the reservoir.

.Another object is to provide o, vertical master cylinder enel reservoir unit in which e greater Bort oi the reservoir is evaileble es n source oi :duid supply.

Another object is to provide en improved braking system incorporating my novel master cylinder.

Other objectsend advantages will become an parent es the description proceeds.

in the Growing,

Fig. 1 lis n sectional elevation showing my new und improved compensating master' cylinder;

Fig.- 2 is e diagrammatic illustration oi e hy drenlic braking system incorporating my .novel Fig. 3 is' an enlarged view of the piston moche nisni shown in Fig. l but showing the parte in `odiderent position.

Referring tothe drawing, l.' heve indicated u y:meester cylinder et which is provided withintegrul lugs t having holt holes. hy means oi which the master cylinder meyloe attached to the freine of an automobile or other suitable support. The upper end of the ter cylinder t is threaded to receive en ennulus l which forms the bese oi the reservoir indicated generally at t. The reservoir is shown es comprising e relatively nerrow strip of motel ii which hes been bent baci; upon itself to provide folds lli which aiiord fienibility to the reservoir.

Above the strict is e sheet metal cup l l which forms the upper part of the reservoir and which cerries a pecking gland l2 through which the piston rod lt passes. 'The piston rod l?! is enor body of the vehicle and where so desired an (Cl. Q30-54.6)

larged at its upper end. as indicated at I4, and has an adjustable extension I5,by which it is connected to foot pedall I6. Beneath the enlargement M is a washer I1 which receives the thrust o a spring i8 resting on the upperend 5 of thecup ii. The spring I8 acts to return the piston rod i3 and pedal I6 to initial position following each application of the brakes.

The foot pedal it is pivoted at I9 to the frame additional spring tu may he provided to insure return of the foot pedal and piston rod to initial position. The initial position of the foot pedal it may he determined by any suitable stop (not shown) or by one end of the slot in the door boord or the vehicie. A Y

A noot 2i hss n steun '2 which extends through the upper end or" the reservoir and serves as a meanstc indienne the height of the uid in the reservoir. The reservoir is lled by unscrewing M20 the plug E5, thereby :morning an opening through which uid muy he introduced into the reservoir. Since the tout ce ci i@ is pivoted about e xed pivot it, the nicher end ci the reservoir will have A c slight interni movement during each epplication or the bruises, This movement is' provided for by the folds it errnedin the enible Astrip t. The reservoir structure disclosed herein is claimed in the conceding application of Erwin lt. Lowelxe.' Seriel No. ileiii, nled Jenz, 1932, issued es Petent No. lel.

The neuster cylinder ti 'nos a. bore 2t, the upper end of which connects directly with the reservoir. :in this loore is e, reciproceble piston, indicated generally by the reierenc'zel numeral te'.

. This piston comprises a. shell 2t and a relatively movehle member which is urged in one direction by the spring which is interposed between opposed surfaces on the shell 2t `und mem# her 2l. Cooperating shoulders te and tu, formed on the shell und member, respectively, limit relative movement of. the shell and member in one direction. sheli i@ is mede of such size that it ts snugly in the bore 2li of the cylinder and this shell is provided with an opening extending entinelyY therethrough. It is in this Vopening that the movable member 2l is located.

The forward end ot the opening through theshellE@ is in the term oi a cylinder 3l in which the forward cylindrical extension 32 of the mov- 50 able member nts snugly when the shell 26v and movable memher 2l ere in the relative positions shown in S. En thm position shoulders 29 and to are in engagement ond the forward face of the extension 32 is inthe piene of the forward lili face of the shell 26 so that these faces form a continuous support for the rubber cup 33 which provides a seal between the shell 26 and the cylinder wally and also between the forward face of the shell 26 'and the forward face. of the cylindrical extension 32 on the movable member 21.

. The cup 33 has a central opening 34 which, in the position of the parts shown in Fig. 1, affords a free communication between thevupper end of the compression chamber and the reservoir. The complete passageway connecting the upper end of the compression chamber with the reservoir comprises the opening 34 through the cup 33, the cylindrical bore 3| in the forward end of the shell 26, the annular space formed between the shell 26 and the member 21l in which the spring 28 is located, and the small bores 35 formed in the member 21. The rest positions of the shell 26 and member 21 are determined by a stop 36 which is in the form of a cap screwed to the upper communicate with the interior of the reservoir.

The annular space 31 which is below the top cap 36, constitutes a sediment trap which may be of any desired depth. A drain plug 3l maybe provided.

The lower end of the piston rod I3 simply rests in the socket formed in the movable member 21 so that the piston rod I3 and pedal I6 may re-` turn to their initial positions faster than the piston 25 is returned to its initial -position at the completion of an application of the brakes. The piston is returned to .initial position by a spring 39 which exerts its upward force against an annular washer 40 located inside the cup 33. The lower end of the spring 36 rests upon a return valve 4I which is normally held against its seat 42 with sumcient force to require a differential in fluid pressure of approximately nine pounds per `square inch to unseat it. The return valve 4I carries an outlet valve 43 which opens under a very light pressure and which isheld in closedl position by a spring 44. K

The outlet end of the master cylinder commucation with the reservoir so that any air which may have found its way into the master cylinderA can rise inthe master cylinder and pass from the highest point of the master cylinder into the uid reservoir. This 'communication between/the interior of the master cylinder andlthe reservoir 5 also compensates for changes in the condition of Y will be displaced from the upper end of the master cylinder and returned 'to the reservoir.

When the brake pedal is depressed the first eect 'is ,to move'` the member 21 until its shoulder 30 comes into engagementwith shoulder 23 of theshell 26. This results in a slight compression of the spring 23 whiclfis purposely madev of less strength than the spring 33. This initial movement of the member 21 relative to the shell Y 26 causes the parts to assume the position shown in Fig. 3, wherein the forward face of the pro- .lection 32 on the member 21 lies in the same plane as the forward face of the shell 26, the

two providing a continuous support for the 'cup 33. This initial movement of the member 21 relathe forward end of the shell 26 and the exten' X sion 32, with less relative movement between these parts.

Continued depression of the foot pedal causes piston rod I3 to move shell 26 and member 21 as a unit downwardly in the bore 24 to discharge fluid from the master cylinder past valve 43 and into conduits 45. This discharge of uid from the master cylinder creates pressure in the conduits and wheel vcylinders and causes the pistons 41 in the wheel cylinders 46 to move the brake shoes 46 into engagement with* the-drums 43. When the operator removes his foot from the pedal I6, lsprings I8 and 2ll\immediately return foot pedal I6 and piston rod I 3, to their 1initial positions. Spring 23 immediately expands, thereby moving member 21 relative toshell 26 and thus opening al passageway through the piston.

Separating movement of member. 21 4and. shell 26, under the influence of spring'` 23 during the return 'stroke of the' piston, is limited by the engagement of shoulder 53 with spring ring 54 whichis snapped into a suitable 'grooveprovided in the upper end of the shell 26.

Spring 33 also expands and pushes the cup 33 and piston back toward initial position. During this return stroke oi' the piston the spring 33v is also exerting pressure on the return valve 4I which serves to restrict the ow of fluid from the conduits and wheel cylinders back into the master cylinder under the influence of the retractile springs 50. Furthermore, the length and smallness of the conduits and the viscosity of the fluid further restrict this return ow of fluid to the master cylinder. The result is that a partial vacuum or condition of sub-atmospheric pressure is created in the master cylinder during kthe return stroke of the piston. and this condition causes fluid to flow fromthereservoir through the piston and hole 34 in the rubber cup 33 into the master cylinder during the return stroke of the piston.

When the master cylinder piston has reached its initial position, as indicated in Fig. 1, there is an excess of 'fluid in the operating parts of the system. As the ,wheel cylinder pistons continue their return to initialor inoperativev position, under the influence of their retractile springs, fluid is continually returned to the master cylinder 'and 'the excess escapes back to the reservoirthrough the opening 34 -in the cup 33 and between the two parts of the piston. This excess fluid carries with it any air which lmayhave -found its way into the operative parts of the system. Because of the fact that the passageway which connects the master cylinder with the reservoir is' located at the very top of the'compression chamber, all air bubbles are completely purged from the master cylinder.

While I have illustrated my invention as incorporated in a single embodiment, it is to be understood that my invention may take many forms and that the scope of my invention is to be limited solely by the following claims.

I claim: I

1. In a hydraulic pressure ysystem of the class described, the combination of a cylinder, a piston therein, said piston comprising relatively movable parts, a spring interposed between said parts, means to advance said piston, a spring in said cylinder for retracting said piston, said lastnamed spring being stronger than said firstnamed spring, and a uid reservoir in communication with the rear of said piston, said movable parts in separated position being conformed to provide a passageway therethrough, which passageway disappears when said parts are moved. to closed position whereby movement between said parts controls communication between said cylinder and said reservoir.

2. In a hydraulic pressure system of the class described, the combination of a compression cylinder, a piston therein comprising relatively movable parts, said parts in one position being conformed to provide an imperfvorate piston and when in a second position being conformed to provide a passageway therebetween, a relatively v light spring for separating said parts to provide a passageway therebetween, means to advance' said piston, a relatively strong spring in said cyl- 'inder for retracting said piston, a single stop for limiting retraction of both parts of said piston and for permitting said irst-named spring to hold said parts in separated relationship, and a uid' reservoir in communication with the rear of said piston, whereby said movable parts control communication between said cylinder and said reservoir.

' Y HERBERT C. BOWEN. 

